State nurseries come top
The inspectors found that services for four-year-olds were satisfactory or better in around 85 per cent of state nursery and primary schools, but in only 55 per cent of the private playgroups and nurseries.
There was a similar difference in teaching quality - teachers in the private sector tended not to work enough alongside children.
The greatest disparity was in curriculum planning, assessment and record-keeping. While at least four out of five state schools reached satisfactory standards, only one in three private playgroups and nurseries did so.
However, children's personal and social development was at least satisfactory, and often good or very good, in more than 85 per cent of settings in both sectors.
The report, based on full inspections of 340 maintained nursery and primary schools and more than 300 non-maintained playgroups and nurseries in 1997-98, states that the overall quality of education for this age group continues to improve - but slowly.
In about one in 10 early-years classes in maintained schools, teachers introduce reading and writing too early to children who do not yet understand that written symbols have sound and meaning.
"Standards and Quality in the Early Years: educational provision for four- year-olds in the maintained and non-maintained sectors," can be obtained from OHMCI, Phase 1, Government Buildings, Ty Glas Road, Llanishen, Cardiff CF14 5FQ.